Patients with diabetes mellitus have increased rates of atherosclerotic vascular disease as well as restonosis following percutaneous coronary interventions. Smooth muscle cell (SMC) proliferation plays a key role in atherosclerosis and restonosis following vascular injury. The long-term goal of this project is to identify the molecular mechanisms regulating the accelerated SMC proliferation in diabetic states in response to injury. Previous studies and our preliminary data suggest that Id3 is an important regulator of enhanced SMC growth in response to injury in diabetic conditions. The studies outlined in this proposal will utilize our culture system to further define the molecular mechanisms whereby glucose regulates Id3-induced SMC growth enhancement (Aim 1). We will collaborate with Dr. Nadler to determine if 12LO is an important mediator in this process. The in vitro studies will be complemented by important in vivo studies. We will determine the pattern of expression and function of Id3 in vivo in 3 diabetic animal models (the obese vs. lean Zucker and ZDF rats, streptozotocin-induced diabetes with our without hyperlipidemia in the swine, and streptozotocin-induced and genetic diabetes in the mouse). (Aims 2 and 3). Each model will allow for unique approaches to test the central hypothesis that glucose-induced enhancement of SMC growth is mediated at least in part through the HLH factor Id3. The Zucker rat will provide for data on expression of Id3, Id3a and p21 in a model of insulin-resistance. The ZDF rat is a diabetic model with hyperglycemia and thus will allow us to test the hypothesis that Id3 mediates accelerated SMC growth in hyperglycemic states in vivo. The rat studies will be performed in collaboration with Dr. Nadler and these animals/tissues will be shared between projects 1 and 3. Aim 2 will provide further in vivo data to determine if Id3 is essential for enhancement of SMC proliferation and if this effect is mediated by 12LO using gene delivery of hammer head ribozymes (in collaboration with Drs. Gu, Rossi, and Nadler in project 1). The swine model from our core allows for confirmation of the expression data in the rodents in a novel pig model of accelerated diabetic vascular disease at baseline and in response to stent deployment. The STZ-induced diabetic mouse and the db/db/ApoE-/- will allow for genetic analysis of the mechanisms of accelerated SMC proliferation and vascular lesion formation in diabetes with and without hyperlipidemia. The Id3-/- mouse will also allow for a genetic approach to determine the importance and function of Id3 in the accelerated lesion formation in diabetic mice. A major strength of this proposal is that it combines in vitro mechanistic studies with in vivo studies and genetic approaches to gain an overall broader understanding of the role of Id3 in the enhanced SMC proliferation in diabetic states.